Sooo may have not been out playing of late, but i bought a used / not working TM M870 during lockdown months back, sold as leaking and having a hash sawn of job done, plus some vom RIS screwed on. The sweetener for me was it coming with an Angry Gun Gas AR stock, which seem to be obsolete for the most part nowadays.
Ordered a few WII TECH & SAT parts at the same time, they arrived a few weeks later from the east.
Basically it was leaking between the receiver and the gas expansion/reservoir inlet, a couple O rings sorted that, then that leak moved forward - with the proper pressure in the expansion cylinder - the nozzle was now leaking, luckily id ordered a WII TECH one
I also ordered a genuine MESA Remington pump grip and cartridge holder through Brownells.
The pump grip took a little bit of TLC with the finger blaster, sorry sander, and gives a much better lump to grip.
I did splash out on the SAT steel shortened outer barrel, to remedy the hash saw job, plus it has the nice finish and trades.
One bonus other M870 users may or may not be aware of - the SAT barrel has a threaded screw hole to screw the block to up front, this is AMAZING as it does away with that PITA nut plate inside the barrel - if youve taken one of these down youll appreciate how great that is!
Also fitted the WII TECH aluminum hop unit and loading nozzle unit, awesome bit of machining that!
I then reinstated the pump lock with WII TECH steel parts, works a charm.
Well chuffed with it, now it all works properly, its most satisfying to operate, and the shot sound is pretty cool.
Will get some nice TM cartridges now it works
Oh yeh and when testing / not fully assembled i managed to shoot that3 way barrel spacer into the garden during strong winds, that was novel haha!